> On Jun 29, 2023, at 9:52 PM, Dai Ngo <dai.ngo@xxxxxxxxxx> wrote:
>
> This patch grants write delegations for OPEN with NFS4_SHARE_ACCESS_WRITE
> if there is no conflict with other OPENs.
>
> Write delegation conflicts with another OPEN, REMOVE, RENAME and SETATTR
> are handled the same as read delegation using notify_change,
> try_break_deleg.
>
> The NFSv4.0 protocol does not enable a server to determine that a
> conflicting GETATTR originated from the client holding the
> delegation versus coming from some other client. With NFSv4.1 and
> later, the SEQUENCE operation that begins each COMPOUND contains a
> client ID, so delegation recall can be safely squelched in this case.
>
> With NFSv4.0, therefore, the server must recall or send a CB_GETATTR
> (per RFC 7530 Section 16.7.5) even when the GETATTR originates from
> the client holding that delegation.
>
> An NFSv4.0 client can trigger a pathological situation if it always
> sends a DELEGRETURN preceded by a conflicting GETATTR in the same
> COMPOUND. COMPOUND execution will always stop at the GETATTR and the
> DELEGRETURN will never get executed. The server eventually revokes
> the delegation, which can result in loss of open or lock state.
>
> Tracepoint added to track whether read or write delegation is granted.
>
> Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
> ---
> fs/nfsd/nfs4state.c | 40 +++++++++++++++++++++++++++++-----------
> fs/nfsd/trace.h | 1 +
> 2 files changed, 30 insertions(+), 11 deletions(-)
>
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index 4c96cfe19531..15b5043eeca5 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -1144,7 +1144,7 @@ static void block_delegations(struct knfsd_fh *fh)
>
> static struct nfs4_delegation *
> alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
> - struct nfs4_clnt_odstate *odstate)
> + struct nfs4_clnt_odstate *odstate, u32 dl_type)
> {
> struct nfs4_delegation *dp;
> long n;
> @@ -1170,7 +1170,7 @@ alloc_init_deleg(struct nfs4_client *clp, struct nfs4_file *fp,
> INIT_LIST_HEAD(&dp->dl_recall_lru);
> dp->dl_clnt_odstate = odstate;
> get_clnt_odstate(odstate);
> - dp->dl_type = NFS4_OPEN_DELEGATE_READ;
> + dp->dl_type = dl_type;
> dp->dl_retries = 1;
> dp->dl_recalled = false;
> nfsd4_init_cb(&dp->dl_recall, dp->dl_stid.sc_client,
> @@ -5451,6 +5451,7 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> struct nfs4_delegation *dp;
> struct nfsd_file *nf;
> struct file_lock *fl;
> + u32 dl_type;
>
> /*
> * The fi_had_conflict and nfs_get_existing_delegation checks
> @@ -5460,7 +5461,13 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> if (fp->fi_had_conflict)
> return ERR_PTR(-EAGAIN);
>
> - nf = find_readable_file(fp);
> + if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE) {
> + nf = find_writeable_file(fp);
> + dl_type = NFS4_OPEN_DELEGATE_WRITE;
> + } else {
> + nf = find_readable_file(fp);
> + dl_type = NFS4_OPEN_DELEGATE_READ;
> + }
> if (!nf) {
> /*
> * We probably could attempt another open and get a read
> @@ -5491,11 +5498,11 @@ nfs4_set_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> return ERR_PTR(status);
>
> status = -ENOMEM;
> - dp = alloc_init_deleg(clp, fp, odstate);
> + dp = alloc_init_deleg(clp, fp, odstate, dl_type);
> if (!dp)
> goto out_delegees;
>
> - fl = nfs4_alloc_init_lease(dp, NFS4_OPEN_DELEGATE_READ);
> + fl = nfs4_alloc_init_lease(dp, dl_type);
> if (!fl)
> goto out_clnt_odstate;
>
> @@ -5570,8 +5577,13 @@ static void nfsd4_open_deleg_none_ext(struct nfsd4_open *open, int status)
> /*
> * Attempt to hand out a delegation.
> *
> - * Note we don't support write delegations, and won't until the vfs has
> - * proper support for them.
> + * Note we don't support write delegations for NFSv4.0 client since the Linux
> + * client behavior is not compliant with RFC 7530 Section 16.7.5 with regard
> + * to handle the conflict GETATTR. It expects the server to look ahead in the
> + * compound (PUTFH, GETATTR, DELEGRETURN) to find a stateid in order to
> + * determine whether the client that sends the GETATTR is the same with the
> + * client that holds the write delegation. RFC 7530 spec does not call for
> + * the server to look ahead in order to service the conflict GETATTR op.
I'll take these 4 for v6.6, and update this comment to match the patch
description as I apply the patches.
> */
> static void
> nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> @@ -5590,8 +5602,6 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> case NFS4_OPEN_CLAIM_PREVIOUS:
> if (!cb_up)
> open->op_recall = 1;
> - if (open->op_delegate_type != NFS4_OPEN_DELEGATE_READ)
> - goto out_no_deleg;
> break;
> case NFS4_OPEN_CLAIM_NULL:
> parent = currentfh;
> @@ -5606,6 +5616,9 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
> goto out_no_deleg;
> if (!cb_up || !(oo->oo_flags & NFS4_OO_CONFIRMED))
> goto out_no_deleg;
> + if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE &&
> + !clp->cl_minorversion)
> + goto out_no_deleg;
> break;
> default:
> goto out_no_deleg;
> @@ -5616,8 +5629,13 @@ nfs4_open_delegation(struct nfsd4_open *open, struct nfs4_ol_stateid *stp,
>
> memcpy(&open->op_delegate_stateid, &dp->dl_stid.sc_stateid, sizeof(dp->dl_stid.sc_stateid));
>
> - trace_nfsd_deleg_read(&dp->dl_stid.sc_stateid);
> - open->op_delegate_type = NFS4_OPEN_DELEGATE_READ;
> + if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE) {
> + open->op_delegate_type = NFS4_OPEN_DELEGATE_WRITE;
> + trace_nfsd_deleg_write(&dp->dl_stid.sc_stateid);
> + } else {
> + open->op_delegate_type = NFS4_OPEN_DELEGATE_READ;
> + trace_nfsd_deleg_read(&dp->dl_stid.sc_stateid);
> + }
> nfs4_put_stid(&dp->dl_stid);
> return;
> out_no_deleg:
> diff --git a/fs/nfsd/trace.h b/fs/nfsd/trace.h
> index 72a906a053dc..56f28364cc6b 100644
> --- a/fs/nfsd/trace.h
> +++ b/fs/nfsd/trace.h
> @@ -607,6 +607,7 @@ DEFINE_STATEID_EVENT(layout_recall_release);
>
> DEFINE_STATEID_EVENT(open);
> DEFINE_STATEID_EVENT(deleg_read);
> +DEFINE_STATEID_EVENT(deleg_write);
> DEFINE_STATEID_EVENT(deleg_return);
> DEFINE_STATEID_EVENT(deleg_recall);
>
> --
> 2.39.3
>
--
Chuck Lever
